Along with the development of communication technology, Next Generation Network (NGN) technology is developing vigorously. In the current NGN, however, it has become a pressing important issue that how to guarantee the quality of data transmission and to quickly detect a link failure, for example, when unclear voice occurs during the data transmission.
To address the above issue, an Operation and Maintenance (OAM) technique has been provided. The technique can automatically detect various failures of network and adopt the corresponding remedial measures to avoid extension of the failures or try the best to eliminate the failures, and diminish or eliminate negative effects brought by the failures. The existing OAM technique primarily includes the Bidirectional Forwarding Detection (BFD) technique and the Multi-Protocol Label Switching (MPLS) OAM technique provided by the Intentional Telecommunications Union (ITU).
The BFD is a Hello mechanism. Refer to “IETF: draft-ietf-bfd-base-00”, “IETF: draft-ietf-bfd-mpls-00” and “IETF: draft-ietf-mpls-lsp-ping-05” disclosed by the Internet Engineering Task Force (IETF) for detail.
FIG. 1 is a schematic link in an NGN network. The BFD technique is herein described with the link between Node A and Node E as shown in FIG. 1. The BFD has two operating modes which may be selected, as well as an additional function that can be used in combination with the two modes.
The primary mode is known as asynchronous mode. In this mode, a BFD session is established between Node A and Node E. Node A and Node E periodically send hello packets, i.e. BFD packets, to one another, and if a number of those packets are not received by the other node, the session is declared to be down.
The second mode is known as Demand mode. In this mode, it is assumed that each node has an independent way of verifying that it has connectivity to the other node. Once a BFD session for detecting a failure is established, Node A or Node E stops sending BFD control packets to the other, except when either node feels the need to verify connectivity explicitly, in which case a short sequence of BFD control packets is sent, and then the protocol quiesces.
An adjunct to both modes is an Echo function. That is, when the Echo function is active, a hello packet transmitted by Node A in such a way as to have the Node E loop the hello packet back. Node A detects whether the hello packet is lost and determines whether a failure occurs in the link between Node A and Node E based on the detection. The echo function may be used with either asynchronous or Demand mode. Since the Echo function is handling the task of detection, the periodical packets may be reduced in the case of asynchronous mode and the hello packet may be eliminated completely in the case of Demand mode.
In addition, the rate of transmission of hello packets may be negotiated between Node A and Node E so as to notify the one another of the rate at which they can receive and send the packets, and eventually determine the rate of transmission of the hello packets.
A BFD control packet is transmitted in a User Datagram Protocol (UDP) packet with the destination port of 3784 and the source port in a range of 49252-65535, while the destination port of a response packet is 3785. The BFD control packet format is as shown in Table 1.
TABLE 101234567890123456789012345. . .VersDiagHDPFCARsvDetect MultLengthMy DiscriminatorYour DiscriminatorDesired Min TX IntervalRequired Min RX IntervalRequired Min Echo RX Interval
The BFD control packet also includes an optional section, and the format of which is as shown in Table 2.
TABLE 201234567890123456789012345. . .Auth TypeAuth LenAuthentication Data
The first lines in above Tables 1 and 2 include the data bits of the packet, and the other lines thereof indicate the name of each field included in the BFD control packet. The description of each field is as shown in Table 3.
TABLE 3Field nameIndicationVersion (Vers)The latest version number of the protocol, and this documentdefines protocol version 0.A diagnostic code specifying the local system's reason for thelast transition of the session from Up to some other state.Values are:Diagnostic(Diag)0—No Diagnostic1—Control Detection Time Expired2—Echo Function Failed3—Neighbor Signaled Session Down4—Forwarding Plane Reset5—Path Down6—Concatenated Path Down7—Administratively Down8-31—Reserved for future useI Hear You (H)This bit is set to 0 if the transmitting system either is notreceiving BFD packets from the remote system, or is in the processof tearing down the BFD session for some reason. This bit is set to 1if the transmitting system believes it is communicating with theremote system.Demand (D)If set, the transmitting system wishes to operate in DemandMode. If clear, the transmitting system does not wish to or is notcapable of operating in Demand Mode.Poll (P)If set, the transmitting system is requesting verification ofconnectivity, or of a parameter change. If clear, thetransmittingsystem is not requesting verification.Final (F)If set, the transmitting system is responding to a received BFDcontrol packet that had the Poll (P) bit set. If clear, the transmittingsystem is not responding to a Poll.Control PlaneIf set, the transmitting system's BFD implementation does notIndependent (C)share fate with its control plane (in other words, BFD isimplemented in the forwarding plane and can continue to functionthrough disruptions in the control plane.) If clear, the transmittingsystem's BFD implementation shares fate with its control plane.AuthenticationIf set, the Authentication Section is present and the session is toPresent (A)be authenticated.Reserved (Rsv)These bits must be zero on transmit, and ignored on receipt.Detect MultDetect time multiplier. The negotiated transmit interval,multiplied by this value, provides the detection time for thetransmitting system in Asynchronous mode.LengthLength of the BFD Control packet, in bytes.MyA unique, nonzero discriminator value generated by theDiscriminatortransmitting system, used to demultiplex multiple BFD sessionsbetween the same pair of systems.Yourhe discriminator received from the corresponding remoteDiscriminatorsystem. This field reflects back the received value of MyDiscriminator, or is zero if that value is unknown.DesiredThis is the minimum interval, in microseconds, that the localMin TX Intervalsystem would like to use when transmitting BFD Control packets.RequiredThis is the minimum interval, in microseconds, betweenMin RX Intervalreceived BFD Control packets that this system is capable ofsupporting.Required MinThis is the minimum interval, in microseconds, betweenEcho RXreceived BFD Echo packets that this system is capable ofIntervalsupporting. If this value is zero, the transmitting system does notsupport the receipt of BFD Echo packets.Auth TypeThe authentication type in use, if the Authentication Present(A) bit is set.0—Reserved1—Simple Password2—Keyed MD53—Meticulous Keyed MD54-255—Reserved for future useAuth LenThe length, in bytes, of the authentication section, including theAuth Type and Auth Len fields.
The BFD also provides a function to detect MPLS Label switched path (LSP). However, the BFD needs to be combined with the LSP ping, and on the initial stage, a connection should be established via the LSP Ping.
The current BFD technique receives more and more support from data communication products, such as a router. The route protocols of mainstream manufacturers have supported or are supporting the fast convergence via BFD fast detection, and all the routers of mainstream manufacturers have supported or are supporting BFD based link detection function.
As the emergence of BFD technique is late, however, the solutions to actual problems in some network applications have not been disclosed. For example, in MPLS LSP detection, there has been no complete solution or no solution at all on how to suppress alarm storms and how to interwork with OAM on other layers, e.g. how to interwork with the link layer Asyncluronous Transfer Mode (ATM) OAM mechanism to provide a detailed protection switching mechanism.
As above disadvantages of BFD, the ITU MPLS OAM mechanism is generally adopted in the MPLS network for failure detection. The ITU MPLS OAM mechanism is only applicable to the MPLS network. As the LSP of MPLS is established in segments and can be nested, suppose that outer layer tunnels LSPab, LSPbc, LSPcd and LSPde as well as an inner layer tunnel LSPae is established between AB, BC, CD, DE and AE, respectively, wherein the tunnel label of LSPae is nested in the label of the outer tunnel labels, that is, in a packet sent from Node A to Node E, the inner label is the label of LSPae and the outer label is the label of each segment of the outer tunnel. An old outer label will be changed to a new label when arriving at a new segment.
Refer to the Y.1710, Y.1711, Y.1712, Y.1713 and Y.1720 of ITUT for the detailed solutions of the ITU MPLS OAM mechanism.
Similar to the BFD, the ITU MPLS OAM mechanism detects a link failure by sending a Hello packet between two nodes. Furthermore, with the label nesting mechanism, some useful mechanisms are added to the MPLS OAM mechanism, which is described below with additional reference to FIG. 1.
1. Forward Defect Indicator (FDI) mechanism. Detect and determine a defect location via the FDI mechanism. As shown in FIG. 1, an OAM packet of MPLS OAM mechanism needs running over the link LSP of AB, BC, CD, DE and AE. The OAM packet is also a Hello packet which is called a Connectivity Verification (CV) packet or a Fast Failure Detection (FFD) packet in the ITUT. When an outer layer tunnel link continuously loses some number of packets in a period of time, the outer layer tunnel link may be invalid. Suppose that the OAM mechanism of LSPbc detects that the link between Node B and Node C is invalid, Node B reports a defect report to a network management device and automatically sends to Node E a FDI packet for reporting that the link LSPbc is invalid, and Node E determines that all inner LSP tunnel links nested in the Link LSPbc are invalid. The network management device determines that the failure point is located between Node B and Node C according to the failure report from Node B. In addition, the FDI mechanism may be used for suppressing alarm storms.
2. Backward Defect Indication (BDI) mechanism. In the FDI, if a return link exists, after receiving the FDI packet, Node E will return a BDI packet to Node A. The BDI packet is used for notifying Node A that the link between Node A and Node E is invalid and the link between Node A and Node E should be switched.
3. The MPLS OAM mechanism may run FDI packets with high detection rate in outer layer tunnels, such as LSPab, LSPbc, LSPcd and LSPde. These outer layer tunnels are relatively important because they carry a number of inner tunnels. The MPLS OAM mechanism runs FDI packets with low detection rate in inner tunnels, such as LSPae. When a failure is detected in an outer tunnel, the outer tunnel will introduce the alarm into the inner tunnels nested in the outer tunnel automatically to reduce resource consumption.
4. The MPLS OAM mechanism may also establish two tunnels, and one of them is used as a backup tunnel. Upon detecting a failure in a link, the link may quickly switch to the backup tunnel to implement the backup function.
At present, data communication devices generally support the BFD because route protocols used by the data communication devices require the BFD, for example, most of the devices in an IP network support the BFD. In terms of transmission devices, such as the devices in an MPLS network, tend to adopt the ITUT MPLS OAM mechanism since these transmission devices are primarily implemented with hardware.
However, no interworking method between the MPLS OAM mechanism of ITUT and the BFD has been provided. Thus, in a hybrid network including the BFD mechanism and the MPLS OAM mechanism, the interworking of two mechanisms has no solution so far, thus a failure of inter-network link may not be detected. Hereinafter the inter-network link refers to a link crossing multiple networks with different detection mechanisms.
For example, the interworking of detecting mechanisms between the IP network and the MPLS network has no solution in the prior art. FIG. 2 shows a schematic illustrating the networking of a hybrid network consisting of an IP network and an MPLS network. As shown in FIG. 2, suppose that the network between N2 and N6 is an MPLS network, and the networks between N0 and N2 as well as between N6 and N8 are IP networks, wherein the BFD mechanism is adopted by the IP network and the MPLS OAM mechanism is adopted by the MPLS network. When a failure is detected, N0 and N8 should be notified. However, since no solution exists for implementing the interworking between the BFD and the MPLS OAM mechanism, N0 may be notified a failure detected between N0 and N2 but N8 is unable to be notified; N8 may be notified a failure detected between N6 and N8 but N0 is unable to be notified; and N2 and N6 may be notified a failure detected between N2 and N6 but N0 and N8 are unable to be notified.